Synchronizing system



5 Sheets-Sheet l Filed Sept. l0, 1940 MII" Inventor- Everhard H. B. Bartelnk,

His Attorheg.

E. H. B. BARTELINK I SYNCHRONIvZIN-G SYSTEM oct. 13, 1'942.

5 sheets-sheet 2 Filed sept. 1o, 1940 tuin" 4U Y Il! |252:

Inventor Everharcl I-. B. Bartelmk, 13;; )f7/Wad@ His Attorheg.

` E. H.B. BARN-:LINK 2,298,864

SYNCHRONIZING `SYSTEM Filed Sept. 10, 1940 5 Sheets-Sheet 5 Oct. 13, 1942.

l lfmverwto: Eve-hard HB. Bartelink His dotovjrwejzg.l

5 Sheets-Sheet 4 1I'. BQIIIL SY-NCHRQNIZING SYSTEM Filed Sept. 10, 1940 E. H. B. BARTELINK mns Oct. 13, 1942;

Oct 13, 1942 E. H. B. BARTELINK SYNCHRONIZING SYSTEM .Fi1ed`sept- 1o, 1940 5 sheets-sheet 5 IN2-Ol is Attorneu.

Patented Oct. 13, 1942 srNoHRoNIzING SYSTEM Everhard H. B. Bartelink, Niskayuna, N. Y., assignor to General Electric Company, a corporation of New York Application September 10, 1940, Serial No. 356,155

(Cl. PYB-7.2)

22 Claims.

My invention relates to a synchronizing system and has particular utility in its application to a television synchronizing system. More specically, it contemplates a method and apparatus whereby the scanning action of a television receiving system may be maintained Yin accurate synchronism with the scanning action of a television transmitting system'. f

In present-day television systems utilizing cathode ray discharge devices for generating the picture signal at the transmitter and for reproducing the image at the receiver, means must be provided for synchronizing their operation. Ordinarily, in the transmitting picture signal generator a horizontal synchronizing signal is generated during each retrace interval following the end of each horizontal line traced by the cathode ray; and during the flyback interval following the end of each traversal of the picture area by the ray, a vertical synchronizing signal is generated. These signals are combined with the video signal, which is representative of the light and shade values' of the image being scanned, and the complete signal is modulated upon a transmitted carrier. second cathode ray is caused to scan a fluorescent screen in a similar pattern. The intensity of this ray is controlled in accordance with the detected videosignals in order to reproduce the image.

The horizontal and vertical synchronizing sigr nals are separated from the video signals and utilized to trigger the horizontal and vertical deflection generators, respectively. In this `way the two cathode rays in the transmitter andreceiver are maintained in synchronism, as is well understood by those skilled in the art.

Since the quality of the reproduced image is a function of the number of lines, the trend has been steadily in the direction of higher line frequencies to improve picture definition. This makes it more difficult to maintain synchronism. The use of interlaced scanning, wherein successive fields are staggered so that the lines of one field are interlaced with the lines of alternate fields, reduces flicker and thus reduces the necessary field frequency, as is well known. However, the problems of synchronization are not thereby simplified; rather, they are aggravated by the necessity of generating more complex synchronizing waves to maintain accurate interlace.I

It is therefore broadly an object of my invention to provide an improved method and means for synchronizing the operation of a signal re- At the receiver a ceiving system with the operation of a signal transmitting system.

It is further a main object of my invention to provide an improved method and means for synchronizing television transmitting and receiving systems.'

It is a more specific object of my invention to provide an improved television synchronizing system in which transmitted horizontal and vertical synchronizing signals are composed of a plurality of component waves whose frequencies are definitely related in aparticular way, whereby the respective signals may be separated from each other at the receiver through frquency discrimination in a simple and effective manner.

Another object of my invention is to provide line and held' synchronizing waves having related, distinctive frequency characteristics, whereby they may readily be distinguished from each other at the receiving apparatus through the use of simple frequency selective circuits and whereby the possibility of any reaction Vbetween them, which might cause loss of synchronism or interlace, is minimized.

A further object of my invention is to provide an improved synchronizing system particularly suitable for use with interlaced television scanning apparatus having any desired degree of interlace, i. e., where any desired number of fields are interlaced to form one complete picture image or frame. v

More specifically, in a preferred form of my invention the horizontal line synchronizing wave is analyzable into a fundamental component frequency wave and harmonics thereof and the vertical field synchronizing wave is resolvable into certain selected ones of said harmonics only. The difference in the frequency characteristics of the respective waves is utilized for differentiating between them at the receiver and for deriving ho-rizontal and vertical synchronizing potentials therefrom.

Furthermore, in accordance with my invention all the synchronizing waves may be of equal amplitude since they are separated from each other by distinguishing between their frequency characteristics.

generating and transmitting the synchronizing waves also remains substantially constant.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, hcwever, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in Which Fig. 1 is a diagrammatic, conventionalized view of a complete television transmitting system embodying my invention; Fig. 2 is a diagrammatic, schematic view of a pulse generator embody my invention and which may constitute an element of the transmitting system of Fig. 1; Fig. 3 is a group of curves illustrating the wave forms of waves developed at various points in the pulse generator circuit illustrated in Fig. 2; Fig. 4 is a diagrammatic, schematic view of an alternative form of pulse generator embodying my invention and which may constitute an element of the transmitting system of Fig. l; Fig. 5 is a group of Curves illustrating the wave forms of waves developed at various points in the pulse generator circuit illustrated in Fig. 4; Fig. 6 is a diagrammatic, conventionalized view of a complete television receiving system embodying my invention; and Figs. 7 and 8 are circuit diagrams cf alternative forms of synchronizing signal separation circuits embodying my invention and which may constitute an element of the receiving system of Fig. 6.

In the television transmitting system illustrated in Fig. 1 a camera tube 30 of well-known form is provided for producing electrical current variations corresponding to the light and shade values of the image to be transmitted. The specific details of the camera tube form no part of my invention and therefore need not be considered. Briefly, means are provided therein for developing and projecting an electron ray 3| against a sensitive mosaic target 32. The ray is caused to scan the target in a well-known manner through the action of suitable ray deflecting means. These deflecting means are represented as pairs of delecting coils 33 and 34 which effect the scanning action along two coordinate axes in response to potentials applied thereto from the horizontal and vertical deflection generators 35 and 36, respectively. The camera tube 3|] may also include the usual elements for controlling, focusing and accelerating the ray.

As the ray 3| scans the target 32, potentials are supplied to the video signal amplifier 31 corresponding to the conditions of illumination of the target at the instant of transversal by the ray. This action is also well known and need not be detailed.

The pulse generator 40, shortly to be described in greater detail, provides means for synchronizing the operation of the horizontal and vertical deection generators 35 and 36 in a well-known manner. Horizontal and vertical synchronizing signals developed in the pulse generator are indicated schematically as being supplied to the respective deection generators 35 and 36 over the conductors 4| and 42. Various forms of apparatus for generating deflecting potentials and for effecting synchronization in response to the synchronizing signals areV well known to the art. A

the block 43. In amplifier 43 the video signals are further amplified and are also combined, first, with the blanking pedestal, and, second, with the composite synchronizing signals (or supersynchronizing signals) which are indicated as being supplied thereto from the pulse generator 40 over the conductors 44 and 45, respectively. Again, the precise mechanism by which the signals are combined is immaterial to the practice of my invention and is omitted to simplify the description and to avoid undue complication of the drawing. Briefly, the blanking pedestal serves to maintain the signal level in the receiver at the level corresponding to black during the intervals between successive lines and elds traversed by the scanning ray 3|. Thus the video signal is eliminated during these intervals. The composite synchronizing wave, to be described in greater detail shortly, is superimposed upon the blanking pedestal so that the synchronizing signals appear beyond the aforementioned level, namely, in the region which corresponds to blacker than black.

The complete signal is supplied to the final stages of the television transmitting apparatus, indicated collectively by the transmitter 46, This comprises conventional apparatus by means of which the complete signal is modulated on a suitable carrier wave to be transmitted from the antenna 41. In the usual case, it may comprise the modulator, oscillator and power amplier stages of the transmitter.

The various elements of the transmission system of Fig. 1 are supplied with power from a suitable power supply source. In order to simplify the drawing, this is indicated schematically by the common power supply source 48.

Fig. 2 illustrates more in detail one form of the pulse generator 40 which may be employed in the system of Fig. 1 for generating synchronizing signals in accordance with my invention. The composite elements of the pulse generator 43 comprise circuit elements Well known to the art. Therefore, in the interest of simplicity and clarity of illustration, these elements have again been indicated only schematically in block form. It is believed that the details of specic circuits suitable for use in my system will readily be apparent to those skilled in the art in View of the following description.

The operation of the pulse generator of Fig. 2 will best be understood when considered in conjunction with the curves of Fig. 3 which represent the wave forms of electrical waves developed at various points in the pulse generator. They are to be considered as having a common horizontal time axis, so that points on the various curves on any particular vertical line, e. g., the dotted vertical line 49, corresponding to instantaneous values of the Various waves at the same instant of time.

The master oscillator 5G in Fig. 2 generates a train of pulses which may, for example, be shaped to have the general form graphically illustrated by the wave 5| in Fig. 3. The term pulsej as used in the specication and appended claims,

is to be taken in its usual sense to describe a sudden amplitude variation in a signal including a departure from a reference Value followed by a subsequent return to substantially the same value after a time interval. The wave 5| is seen to comprise a series of identical pulses 5|a, of substantially rectangular wave form, which recur at uniform time intervals.

The output from the master oscillator is supplied to a multi-vibrator 52. In a manner well known to the art, this multi-vibrator 52 may be designed to generate a wave of a form which is similar to that generated by the oscillator 50. As shown in Fig. 3, this wave 53 consists of a series of pulses 53a which recur at intervals corresponding to a sub-multiple of the frequency of recurrence of the pulses Ia. These pulses will be synchronized rigidly with the pulses 51a from the master oscillator 50. In the particular illustration it will be observed that the pulses 53a recur at a frequency one half that of the recurrence of the pulses 51a. Also, for reasons that will shortly appear, the wave 53 has a fundamental frequency equal to the line scanning frequency.

The output of the multi-vibrator 52 is also impressed on a chain of multi-vibrators 54, 55 and 56 by means of which waves of successively decreasing fundamental frequency are produced. Each one of these waves has a fundamental frequency which is a submultiple of the fundamental frequency of the output wave of the preceding multi-vibrator. In this way all of the multi-vibrators are maintained in rigid synchronisrn, as is well understood in the art. The final wave 51 generated in the multi-vibrator 53 is of much lower fundamental frequency than the wave 5I and each pulse 51a lasts during the time interval T between the completion of one picture eld and the start of a following field. The wave 51 has a fundamental frequency equal to the eld frequency and is synchronized therewith.

The waves 5|, 53 and 51 are the components of the composite synchronizing signal applied to the amplifier 43 in Fig. l over the conductor 45. The i manner in which they are combined to form the desired composite synchronizing wave will now be outlined.

The outputs of the multi-vibrators 52 and 53 are both supplied to a mixer-clipper 58 in which the waves 53 and 51 are combined to form the wave 59. Various mixer-clipper circuits foraccomplishing this result are known to those skilled in the art and the particular details are of no importance. Brieiiy, in one known form of circuit the wave 51 is added, in reversed polarity, to the wave 53. The resultant signal is applied to the grid of an amplifying device in which the grid voltage is adjusted in such a way that the device is driven beyond cutoff whenever this negi ative output wave 51 appears. The resultant is the wave 5!) which corresponds to the wave 53 except that it is interrupted entirely during the time interval T in which a pulse 51a occurs.`

The outputs of the multi-vibrators and 5Fl are supplied to the mixer-clipper Bil in Fig. 2. In the mixer-clipper 60 the waves 5i and 51 are added in the same polarity and clipped to produce the resultant wave 6l, which corresponds to the wave 5I except that it is switched on only during 2 the time interval T in which a pulse 51ol occurs. The waves 59 and El are then combined to form the nal composite synchronizing signal 62. The

resultant wave 52 may optionally be clipped in y, the clipper 63 before it is applied to the conductor 45, to insure that all pulses are of equal height.

It will be observed from Fig. 3 that the composite synchronizing signal comprises a series of the pulses 53al which recur at line frequency. These pulses 53a are generated continuously except during each period of vertical synchronization between successive picture elds. During this time interval T the pulses 5Ia are transmitted. As previously mentioned, these pulses 51a recur at some frequency which is a multiple of the line frequency. In other words, the fundamental frequency of the synchronizing wave transmitted during the vertical synchronizing interval T is a multiple of the fundamental frequency of the wave transmitted during the remainder of the time. The manner in which this composite wave may be utilized in a television receiver, to effect horizontal and vertical synchronization of the cathode ray therein, will be reserved for discussion in connection with the description of the receiving system of Fig. 6.

s As is indicated by the dashed lines in Fig. 2, the output of multi-vibrator 52, which comprises pulses recurring at the line frequency, may be supplied over the conductor 4l for synchronizing the horizontal defiection generator 35. Similarly the output of the multi-vibrator 56, which comprises pulses recurring at the eld frequency, may be supplied over the conductor 42 to synchronize the vertical deflection generator 33. The outputs of these two multi-vibrators may further be combined to form the blanking pedestal which is applied to the conductor 44. This is schematically illustrated in Fig. 2 by the dashed rectangle which represents a pedestal mixer, and bears that legend, for carrying out this function. The details of these elements of the circuit of Fig. 2 are not material to my invention and are merely mentioned very briefly for the sake of completeness.

The circuit of Fig. 2, just described, is particularly adapted for use in a television system which does not employ interlaced scanning. It is readily adapted to interlaced scanning by making one slight modification, i. e., by synchronizing multivibrator 54 directly from the master oscillator 50. This alternative connection is indicated in Fig. 2 as being made by moving a switch 64 to the lower position. The frequency relationships between the various pulse generating elements will of course also be somewhat different for interlaced scanning, as will be apparent to those skilled in the art without further elaboration.

Fig. 4 illustrates diagrammatically an alternative form of the impulse generator 43 which is particularly suited for employment in the transmitting system of Fig. l when interlaced scanning is used. The curves of Fig. 5 will be considered in conjunction with Fig. 4 in outlining the operation of this form of the impulse generator. As in the case of the curves of Fig. 3, the curves of Fig. 5 are to be regarded as having a common horizontal time axis.

The master oscillator 13 in Fig. 4 generates a train of pulses which, for example, may be shaped into the general form illustrated by the wave 1I in Fig. 5. The output of the master oscillator 1i] is utilized to synchronize the multi-vibrator 12. The fundamental frequency of the output wave 13 of this multi-vibrator is a sub-multiple of the fundamental frequency of the wave 1 I. As illustrated, the pulses 13a recur at a frequency one half that of the recurrence of the pulses lia.

The output of the multi-vibrator 12 is impressed on the multi-vibrator 14, which generates the waves 15. The frequency with which the pulses 15u recur is a lower sub-multiple of the fundamental frequency of the wave 1| than in the case of the wave 13 and, for reasons which will shortly be apparent, the fundamental frequency of the wave 15 is made equal to the line `scanning frequency. As illustrated, the pulses 15a recur at a frequency one fourth the frequency of recurrence of the pulses 1la.

The output of the multi-vibrator 12 is further impressed on a chain of multi-vibrators i5, 11, and 18 by means of which waves of successively decreasing fundamental frequency are produced. As in the case of the multi-vibrators 551, 55 and 56 of Fig. 2, each one of these waves has a fundamental frequency which is a sub-multiple of the preceding multi-vibrator, whereby all of the multi-vibrators are maintained in rigid synchronism with the master oscillator 18. The wave 'la generated in the multi-vibrator 18 comprises pulses '19a which recur at the field frequency and each of which lasts during the time interval T between the completion of one picture eld and the start of a following eld.

The output of the multi-vibrator 'i8 is supplied through a suitable delay circuit 88 to synchronize a multi-vibrator 8i. The wave 82 generated by this multi-vibrator comprises pulses 82a which recur at the same fundamental frequency as the pulses 'ita but which are delayed and narrowed with respect to the pulses a so that each pulse 82a is developed during the shorter time interval t. Apparatus by which this result may be accomplished is well known to the art and will not be discussed here. For example, one suitable circuit for carrying out this function is described in Patent No. 2,132,555, John P. Smith, issued October 11, 1938.

The waves 1I, 13, 15, 'i8 and 82 are the components of the composite synchronizing signal impressed on the amplifier E3, in Fig. 1, over the conductor 415. The manner in which they are combined to form the desired signal is similar to that previously described in connection with Figs. 2 and 3, although somewhat more complicated.

The outputs of the multi-vibrators i8 and T4 are both supplied to the mixer-clipper 83 in which the wave 19, in reversed polarity, is added to the wave 'l5 and the resultant clipped to form the wave 34. This wave corresponds to the wave l5 except that it is interrupted during the time interval T in which a pulse ISa occurs.

The outputs of the multi-vibrators l2 and 18 are impressed on the mixer-clipper 85 in which the waves i3 and 'i9 are added together and clipped to form the wave St. This wave corresponds to the wave 13 except that it is switched cn only during the time interval T in which a pulse 19a occurs.

The output of the multi-vibrator 8l and the output of the mixer-clipper 85 are supplied to the mixer-clipper 8l, in which the wave 82, in reversed polarity, is added to the wave 8S and the resultant clipped to form the wave 88. This wave also corresponds to the wave 'i3 except that it is, first, switched on only during the time interval T in which a pulse 19a occurs and, second, interrupted during the intervening time interval i in which a pulse 82a occurs.

The output of the master oscillator 18 and the output of the multi-vibrator 8| are impressed on the mixer clipper 39 in which the wave 82 is added to the wave 'il and the resultant clipped to form the wave 98. This wave corresponds to the wave 'Il except that it is switched on only during the time interval t in which a pulse 82a occurs.

The outputs of the three mixer-clippers 33, 81

and S9 are combined to form the final composite synchronizing signal 9i. The resultant wave 9| may optionally be clipped in the clipper 92 before it is supplied to the conductor 45 to insure that all pulses are of equal height.

In the composite wave 9i the pulses 15a, which recur at line frequency, are those through which' horizontal synchronization is accomplished. The pulses '13a constitute the so-called equalizing pulses which are commonly employed in interlaced scanning systems to improve the stability of interlace. The particular wave 9| illustrated is suitable for a system of double interlaced scanning, i. e., one in which two successive interlaced fields are required to produce a single complete picture image or frame. The composite synchronizing wave @l is represented in the vicinity of the time interval including the end of one picture field and the start of the next field. In wave 92 the synchronizing wave is represented in the vicinity of the end of an alternate picture field. If we consider the beginning of pulse 19a as a reference point, it will be observed that the horizontal synchronizing pulses 15a in the respective portions of the waves Si and 92 are displaced from each other in time by one-half the interval of recurrence. This is necessary in order to obtain proper interlace, as is well known to those skilled in the art. The function of the equalizing pulses f3 is to remove all influence of the unequal time intervals between the pulses '55a and 19a in alternate fields. This feature per se is well known in the art and forms no part of my invention. For a further understanding of the function of the equalizing pulses, reference may be had to Patent No. 2,192,121, Alda V. Bedford, issued February 27, 1940.

The time interval T, during which the pulses 73a and 'Ila occur in waves 9| and 92, is that of a vertical pedestal. The intervening interval t, during which the pulses ia occur, is that of a Vertical synchronizing signal. Thus, as is illustrated in waves 9i and 92, the pulses 'Ha which have a fundamental frequency which is four times the fundamental frequency of the pulses 15a, are transmitted during the vertical synchronizing period t. The equalizing pulses 13a, which have a fundamental frequency which is twice the fundamental frequency of the pulses 15a, are transmitted during that portion of the time period T of the vertical pedestal preceding and following the vertical synchronizing period t.

As is indicated by the dashed lines in Fig. 4,

the output of the multi-vibrator 'i2 may be supplied to a multi-vibrator 93 which generates thc horizontal synchronizing pulses recurring at the horizontal line frequency. The output of this multi-vibrator may be supplied over the conductor lil for synchronizing the horizontal deflection generator of Fig. 1. The output of the multi-vibrator "i8, which comprises the broad pulses 79a recurring at field frequency during the time interval T between successive fields, may be employed to form the pedestal. The outputs of the multi-vibrators 78 and 93 may be combined in the pedestal mixer 94 and applied to the conductor iii as illustrated. As in the case of the pulse generator of Fig. 2, the details of these elements of the pulse generator circuit are not material to an understanding of my invention and are mentioned only for the sake of completeness.

The synchronizing waves applied to the deection generators 35 and 36 over the conductors di and 42, the blanking pedestal supplied over conductor titi, and the synchronizing signals supplied over conductor are all synchronized with the master oscillator in the pulse generator 48. Therefore, as will be understood by those skilled in the art, all the components of the final wave transmitted from the antenna 41 of Fig. 1 are maintained in their proper relationship.

The manner in which the transmitted synchronizing waves, as described above, are utilized at receiving apparatus will best be understood when considered in conjunction with the television receiving system illustrated in Figs. 6, 7, and 8.

Referring now to Fig. 6, the transmitted signal is received by the antenna |00. The initial stages of the television receiver apparatus are indicated collectively by the block |I. These may be conventional, comprising in the usual case the high frequency amplifier, oscillator, demodulator, and power amplifier circuits of the receiver. The demodulated television signal is supplied over the' conductor |02 to the control element |03 of a cathode raydischarge device |04, by means of which an image corresponding to the received signal is reconstructed.

The cathode ray device |04 may be of any well known form and the details thereof form no part of my invention. Briefly, means are provided therein for developing and projecting an electron ray |05 against a fluorescent screen IM on the end of the envelope. The intensity of the ray is varied in accordance with the signals applied to the control element |03. At the same time the ray is caused to scan the screen |06 in a pattern similar to that traced by the cathode ray 3| in the transmitter. This action is effected by deiiecting the ray along coordinate axes by suitable means, illustrated as pairs of magnetic defiecting coils Il and I d8. Currents for energizing the deflecting coils |01 and |00 are supplied by the horizontal and vertical defiection generators lili? and llt, respectively.

The synchronizing signals, which also appear in the output of the television receiver |01, are clipped from the video signals in the synchronizing signal clipper III and supplied over the conductors I i2 to the synchronizing signal separation circuit H3, to be described shortly in greater detail. In the separation circuit ||3, horizontal and vertical synchronizing potentials are developed. These are indicated schematically as being supplied to the respective defiection generators le@ and Ill) over the conductors H4 and H5. As is well known in the art, these potentials are utilized to trigger the deection generators at the proper instants of time in order to effect synchronization of the scanning action.

The various elements of the receiving system of Fig. 6 are supplied with power from a suitable source, indicated schematically by lthe power supply source 99.

Fig. '7 represents one particular form of synchronizing signal separation circuit ||3 which may be employed in the system of Fig. 6. This circuit discriminates between the horizontal and vertical synchronizing signals and separates them from each other. This separating action depends upon the frequency characteristics, i. e., the wave form, of the received composite synchronizing signal, and the function of the circuit will be better understood if the character of this signal is first considered.

Assume that the received composite synchronizing wave is of the wave form illustrated by the wave 62 of Fig. 3. The individual pulses contained in this wave are all substantially rectangular in shape. It is well known that any nonsinusoidal periodic wave may be resolved into a Fourier series of component waves, each of simple sinusoidal wave form. It is also a demonstrable fact that a periodic wave composed of identical rectangular pulses recurring at regular intervals is analyzable into a fundamental sine wave, having a frequency equal to the rate at which the identical pulses recur, plus an almost infinite number of sine waves whose frequencies are different harmonics of the fundamental. Thus, the frequency of recurrence of the identical pulses determines the lowest frequency present in the sine waves of the series. The amplitude and duration of the individual pulses determine the magnitudes of the component waves and the particular harmonics present. Distortion of the rectangular wave form will not eliminate the fundamental though the magnitudes of the various component waves and the particular harmonics present will be altered. These sine waves of the Fourier series are not merely abstract mathematical quantities. They are physically realizable electrical waves which may easily be derived from the non-sinusoidal rectangular waves by suitable circuits.

Referring again to Fig. 7, assume that the composite synchronizingI signal 62 of Fig. 3 is impressed on the conductors I I2. This'signal is applied through the conductor I I4 to the horizontal defiection generator |09 in order to synchronize it at the fundamental frequency of the pulses 53a. It will be recalled that during the vertical synchronizing interval T the pulses 53a disappear, and the pulses Ela are substituted. These pulses have a higher fundamental frequency which is a harmonic of the pulses 53a, as previously explained. In the particular wave illustrated in Fig. 3 it is the second harmonic. It will be observed that the leading edges of alternate pulses 5Ia| recur at precisely the same time intervals as the leading edges of the pulses 53a. As is well known to the art, it is a simple matter to keep the deflection generator |09 synchronized in accordance with alternate pulses Ela providing that these double frequency pulses have the correct leading edges and are present during the time interval T.

The signal received on conductors ||2 is also impressed, through a series resistor I I1, upon the tuned circuit II6 comprising an inductance and capacitor in parallel. This circuit is tuned to the fundamental frequency of the pulses 53a. Therefore, it has a high impedance to waves of that frequency and a very low impedance to waves of higher frequency, these latter being effectively grounded through the capacitor. Consequently, this tuned circuit is effective to separate the fundamental frequency component of the pulses 53a from the other harmonic components of the Fourier series composing the pulses 53a.

'As long as the pulses 53a are received, oscillating potentials at their fundamental frequency appear across the tuned circuit IIS. These potentials are applied, by means of a grid capacitor I I8 and grid resistor I I9 upon the control grid of a thermionic amplifier |20. The amplier |20 is biased to operate as a grid detector and, in a manner well known to the art, the potentials impressed thereon from the tuned circuit I|6 are rectified. The time constant of the capacitor ||8 and resistor IIS is long compared to the period of recurrence of the pulses 53a, so that the rectified potentials maintain a substantially constant bias on the grid as long as the pulses 53a are impressed on the circuit. The anode potential of the amplifier |20 therefore remains substantially constant. Any ripple at this frequency appearing in the anode circuit may further be filtered from conductor I by means of the resistor 2| and by-pass capacitor |22.

Now assume that a vertical synchronizing interval occurs, as is indicated by the time interval T in Fig. 3. The pulses Sla. are now impressed upon the separation circuit of Fig. 7. The fundamental frequency of these pulses, as previously explained, is twice the frequency of pulses 53a and thus twice the resonant frequency of tuned circuit H0. Since the impedance of the tuned circuit is very low for any frequency higher than its resonant frequency, the potential impressed on the grid of amplier i 2:0 is suddenly decreased. The result is a transient variation in anode potential. This transient variation is transmitted as a pulse through the blocking capacitor |23 and resistor |2| to the conductor I5. Therefore, a pulse is impressed upon the vertical deiiection generator I0 at every time interval T, in accordance with the transmitted signals.

When an interlaced picture is to be transmitted, the fact that there is a different time interval in alternate fields between the beginning of the vertical synchronizing interval T and the nearest horizontal synchronizing pulse may affect the quality of the interlace. One method of circumventing this trouble is to use the trailing edge of each vertical pulse for synchronization, rather than the leading edge.

Another method is to transmit the synchronizing signal 3|, 92 of Fig. 5 and to tune the resonant circuit HB of Fig. 7 to twice the fundamental frequency of the pulses 15a, i. e., to the fundamental frequency of the pulses 73a. Since this frequency is present in both Waves, oscillating potentials will be developed across tuned circuit IIB when either pulses 15a or 13a are received. In the preferred forms of waves illustrated in Fig. 5, the Widths of pulses 75a. and i3d are made inversely proportional to their frequency of recurrence. It can easily be shown that, under these conditions, the amplitude of the oscillating potentials `developed across tuned circuit IIB is constant irrespective of whether pulses a or 13a are received. Thus, no transient change in anode potential of device I 20 occurs upon the transition from one group of pulses to the other. In some cases, it may be desired to make pulses 75a and 13a of equal widths. In this case the potential across tuned circuit H6 will increase at the beginning of time interval T and a transient pulse Will be developed in the anode circuit of device 20. However, the resultant pulse transmitted to theverticaldefiectiongenerator Hi) is of opposite polarity to the pulse developed at the beginning of the vertical synchronizing interval t and will not tend to cause false triggering of the generator H0.

A slightly different form of synchronizing pulse separation circuit ||3 may be employed in the receiving system of Fig. 6 to provide additional protection against false vertical tripping. A circuit which will accomplish this is shown in Fig. 8.

In Fig. 8 the composite synchronizing signal 9|, 92 `of Fig. 5 is impressed upon two separate tuned circuits |30 and |3| through the series resistors |32 and |33 respectively. The circuit |30 is tuned to the fundamental frequency of the pulses 75a, whereas the circuit |3| is tuned to the fundamental frequency of the pulses 13a. The composite signal is also supplied over the conductor lill in order to synchronize the horizontal defiection generator |09 in the same manner as previously described in connection with the circuit of Fig. 7.

A portion of the potential appearing across the tuned circuit |30 is rectified by the diode detector circuit comprising the resistor |34, capacitor |35 and diode rectifier |35. A portion of the poten.- tial appearing across the tuned circuit |3| is also rectified by a similar diode detector circuit comprising the resistor |31, capacitor |38 and diode rectifier |39.

Potentials developed in the tuned circuits |30, |3| and rectified by the respective diodes |36 and |39 are impressed upon control elements of the thermionic amplifier |40, which is illustrated as of the pentode type. As shown, the anode of diode |30 is coupled to the screen grid |4| of the amplifier |40 through a coupling capacitor |42. A suitable positive potential is impressed on the screen grid |4| from a potential source, not shown, through a decoupling resistor |43.

The anode of diode |39 is coupled to the control grid |44 of the amplifier |40 by means of a grid capacitor |45 and grid resistor |46. The control grid |44 is also supplied with a suitable negative bias from a suitable potential source, not shown.

The operation of the separation circuit of Fig. 8 upon reception of the composite synchronizing wave 9|, 32 is as follows: Assume first that pulses 15a are received. These cause oscillating potentials to be developed in the tuned circuit |30 which are rectified and applied through the capacitor |42 to the screen grid |4| in a negative sense. The time. constant of the capacitor |42 and resistor |43 is sufiiciently great so that this negative potential remains substantially constant over a vertical or framing interval and at a value sufiicient to bias the amplifier |40 to an inoperative condition.

Assuming next that a group of equalizing pulses 73a are received, an oscillating potential is de veloped across the tuned circuit I3 I, rectified and applied through the capacitor |45 to the control grid |44 of the amplifier |40. This potential is applied to the grid |44 in a negative sense and is again of a value sufficient to maintain the amplifier |40 inoperative. Thus, when either the horizontal synchronizing pulses a or the equalizing pulses 73a are received, no current flows in the anode circuit of the amplifier |40.

Assume neXt that a group of vertical synchronizing pulses 'Ha is received. The potential applied to the grid |44 from the diode |39 disappears, since there is no component frequency present in the pulses Tia equal to the resonant frequency of the tuned circuit |3|. Likewise, there is no component frequency present in these pulses equal to the resonant frequency of the tuned circuit |30, so no potential is applied to the screen grid |4| from the diode |36. The amplifier |40 is therefore unblocked and draws anode current. The result is a transient decrease in anode potential which is transmitted as a pulse through the blocking capacitor |41 and resistor |48 to the conductor H5. This pulse of voltage is effective to synchronize the vertical delection generator H0, as previously described. Any ripple in this pulse due to frequencies present in the pulses 'Ila may be filtered from the conductor ||5 by the resistor |48 and a Icy-pass capacitor |49.

It might also be noted at this point that the tuned circuit |30 and associated elements |32, |34, |35, |36, and |42 can be omitted entirely, if desired, to simplify the circuit. The operation of' the circuit is then essentially the same as previously described in connection with the modied form of the circuit of Fig. 7 wherein the circuit I I6 is tuned to the fundamental frequency of the pulses i3d for operation with the synchronizing signal 9|, 92 of Fig. 5. However, the circuit of Fig. 8 provides additional protection against false vertical tripping by reason of the fact that either one of the negative biasing potentials applied to the respective grids prevents change in anode potential of amplifier |49 until the vertical synchronizing pulses are received.

While the diodes |36 and |39 and the pentode |40 have been illustrated as separate devices, these elements may conveniently be combined in aI single dupleX-diode-pentode tube having a common cathode for the three groups of electrode elements.

In the specific form of synchronizing signal illustrated in Fig. 3 the Vertical synchronizing pulses recur at twice the frequency of the horizontal synchronizing pulses. Similarly, in the specific form of synchronizing signal illustrated in Fig. 5 the vertical synchronizing pulses recur at four times the frequency of the horizontal synchronizing pulses and the equalizing pulses at twice this frequency. Of course these particular values are not limiting. The frequency relationships of the various pulses can be 'generalized as set forth below.

Consider first the general form of synchronizing signal, which may be utilized in a system op-l erating either with or without interlaced scanning, but without equalizing pulses. If the fundamental frequency of the horizontal synchronizing pulses is fh, it is necessary to make the fundamental frequency component of the vertical synchronizing pulses equal to pfh where p is any integer greater than unity. This insures that there will be no frequency component equal to fh in the synchronizing signal during the vertical synchronizing period and enables the two signals to be separated in a simple frequency detecting circuit such as that of Fig. 7.

In the event that the synchronizing signal is utilized in an interlaced scanning system in which it is also desired to transmit equalizing pulses, the fundamental frequency of the vertical synchronizing pulses must be made equal to plcnfh, where p is any integer greater than unity, where 7c is any integer, where 11, is the number of interlaced picture fields in which one image is completely scanned and where fh is the fundamental frequency of the horizontal synchronizing pulses. The fundamental frequency of the equalizing pulses will then be knfh. The signals may be separated from each other by a circuit such as is shown in Figs. '7 and 8. If the circuit of Fig. 'l is used, then the circuit H6 should be tuned to knfhz, since there is no frequency component present which is equal either to fh or lcnfh when the vertical synchronizing pulses, having a higher fundament-al frequency plcnh, are transmitted.

In the foregoing analysis the frequency fh of the horizontal synchronizing pulses has been indicated as being the same as the line scanning frequency. While ordinarily it is preferable to have these two frequencies the same for practical reasons, there is no reason why ,in cannot be an integral multiple of the line scanning frequency. The above generalizations are then still valid, since potentials are continuously available for synchronizing the horizontal deiiection generator by reason of the harmonic relationship between the line scanning frequency and all synchronizing signals.

In both the illustrated embodiments of the invention, the widths of the individual pulses in the synchronizing waves have been illustrated as being inversely proportional to their frequencies of recurrence. Thus, in Fig. 3, the pulses Ela are illustrated as being of half the width of the pulses 53a. Similarly, in Fig. 5, the pulses lla and 13a are illustrated as being one-fourth and one-half the widths of the pulses 15a, respectively. Therefore, except for the slight dissimilarity between the synchronizing signals 9| and 92 of alternate frames in the vicinities of the initiation and termination of the time interval T, the average amplitude of the synchronizing signals remains substantially constant.

It has been pointed out previously that the illustrated relationship of pulse widths may be desirable when the synchronizing signal separation circuit of Fig. '7 is adapted to derive vertical synchronizing pulses from a signal containing equ'alizing pulses. This refinement also has the further advantage that the average amplitude of the composite synchronizing signal, as well as its maximum amplitude, is always substantially constant. Consequently, the apparatus for generating and transmitting the synchronizing signal may be designed for high efciency operation on a substantially constant load.

Various well known forms of apparatus are available for generating pulses of any desired ratio of pulse width to frequency, and their design will be apparent to those skilled in the art without further elaboration.

While my invention has been described in its application to a television system, wherein it possesses particular utility, it will be apparent that it may also find utility in other forms of signalling systems. Broadly considered, my invention is applicable to electrical signalling systems in which a plurality of control signals are sequentially transmitted over a single channel, separated from each other at a receiving station and utilized to effect several individual and distinct indicating or controlling operations.

It will also be apparent from the foregoing description that the frequency band required to accommodate the synchronizing signals need not be unduly wide.v Complete separation of the different signals is achieved even though their lfundamental frequencies are separated from each other only in the` ratios of small whole numbers. Thus, in the specific synchronizing signal illustrated in Fig. 3, the fundamental frequency of the wave 5| is only twice that of wave 53. Similarly, in Fig. 5 the fundamental frequency of wave 7| need only be four times that of Wave l5 for a complete double interlaced scanning system utilizing equalizing pulses. The separation of the various signals may be secured without any possibility of interaction or false operation by virtue of the fact that each signal contains no frequency component whatsoever lower than its fundamental frequency.

Vhile I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, `and I contemplate by the appended claims to cover any such modifi-cations as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In the art of television, the method of providing a composite synchronizing signal for use in a system employing interlaced scanning ccmprising the steps of developing first synchronizing pulses recurring at a frequency fh equal to the line scanning frequency or an integral multiple thereof and synchronized with successive scanning lines, interrupting said pulses during the time intervals between successive picture fields, developing equalizing pulses during said last mentioned intervals recurring at a frequency lcnfh, where k is an integer and 1i is the number of interlaced picture fields in which the picture area is completely scanned once, interrupting said equalizing pulses during an intervening portion of each of said last mentioned intervals, developing second synchronizing pulses during said intervening portions recurring at a frequency pk'rLfh, where p is an integer greater than one, and combining said pulses to form a coinposite synchronizing signal.

2. In the art of television, the method of providing a composite synchronizing signal for use in a system employing interlaced scanning comprising the steps of developing substantially rectangular line synchronizing pulses which are synchronized with the intervals between successive trains of picture signals representative of lines of an image to be transmitted and which recur at a frequency fh, interrupting said pulses during the time intervals between Successive picture fields, developing substantially rectangular equalizing pulses during said last-mentioned intervals which recur at a fundamental frequency knfh, where lc is an integer and n is the number of interlaced picture fields in which said image is completely scanned, interrupting said equalizing pulses during an intervening portion of each of said last-mentioned intervals, developing substantially rectangular field synchronizing pulses during said intervening portions which recur at a fundamental frequency Pknfh, where p is an integer greater than one, and combining said pulses to form a composite synchronizing signal.

3. In the art of television, the method of providing a composite synchronizing signal cornprising the steps of developing substantially rectangular line synchronizing pulses which are synchronized with the intervals between successive trains of picture signals representative of lines of an image to be transmitted and which recur at a frequency fh, interrupting said pulses for a predetermined time during each of the time intervals between successive picture fields, developing substantially rectangular field synchronizing pulses in said last-mentioned intervals which recur at a fundamental frequency 10ft, where p is an integer greater than one, and combining said synchronizing pulses to form a composite synchronizing signal, al1 said pulses being of substantially equal heights and of widths inversely proportional to their frequencies of recurrence, whereby the average amplitude of said signal is substantially constant.

4. In the art of television, the method of providing a composite synchronizing signal for use in a sytem employing interlaced scanning comprising the steps of developing substantially rectangular line synchronizing pulses which are synchronized with the intervals between successive trains of picture signals representative of lines of an image to be transmitted and which recur at a frequency fh, interrupting said pulses during the time intervals between successive picture fields, developing substantially rectangular equalizing pulses during said last-mentioned intervals which recur at a fundamental frequency knfh, where lc is an integer and n is the number of interlaced picture fields in which said image is completely scanned once, interrupting said equalizing pulses during an intervening portion of each of said last-mentioned intervals, developing substantially rectangular field synchronizing pulses during said intervening portions which recur at a fundamental frequency pknfh, where p is an integer greater than one, and combining said pulses to form a composite synchronizing signal, all said pulses being of substantially equal heights and of widths inversely proportional to their frequencies of recurrence, whereby the average amplitude of said signal is substantially constant.

5. In a television system, a synchronizing pulse generator for synthesizing a composite synchronizing signal comprising, in combination, first means for generating a first series of substantially rectangular pulses recurring periodically at a frequency pfh, where p is an integer greater than one and fh is the frequency of horizontal scanning or an integral multiple thereof, second means for generating a second series of substantially rectangular pulses recurring periodically at the frequency fh, said pulses allbeing of substantially equal heights and of widths inversely proportional to their frequencies of recurrence, whereby the average amplitude of both said series is substantially the same, third means for generating a third series of substantially rectangular pulses recurring at the frequency of vertical scanning, means for transmitting said first series of pulses and for interrupting their transmission during the time intervals between the pulses of said third series, means for transmitting said second series of pulses and for interrupting their transmission during the time durations of the pulses in said third series, and means for combining said interrupted series of transmitted pulses to form a continuously transmitted composite synchronizing signal.

6. A television synchronizing system comprising, in combination, means for generating a first series of pulses synchronized with the intervals etween successive scanning lines and recurring periodically at frequencies equal to the line scanning frequency or to an integral multiple thereof, means for generating a second series of pulses synchronized with said first series and recurring periodically at a frequency equal to a higher integral multiple of said line scanning frequency, means for transmitting said rst series, means for interrupting the transmission of said first series for predetermined time intervals occurring between successive picture fields and for transmitting said second series during each of said intervals, means for receiving said transmitted pulses, a line deflection generator adapted to be synchronized at any of said frequencies, means supplying all said received pulses to said generator for continuously synchronizing its operation, means for deriving a field synchronizing pulse from said received pulses in response to the disappearance of a component frequency of said rst pulses during said intervals, said component frequency being lower than the frequency of recurrence of the pulses in said second series, a field deflection generator adapted to be synchronized at the frequency of recurrence of said field synchronizing pulses, and means supplying said field synchronizing pulses to said field deection generator for synchronizing its operation.

7. In a television system having means for receiving a continuous composite synchronizing signal, said signal being composed of a plurality of electrical waves consecutively arranged in a predetermined time sequence, certain of said waves containing components of a particular frequency and higher frequency harmonics thereof, at least one other of said waves being composed only of higher frequency harmonics of said frequency, means for impressing said signal upon a frequency responsive device, said device being adapted to develop substantial voltages during intervals when said frequency is present in said signal and relatively low voltages during intervals when said frequency is absent, and means responsive to the transient decrease in said voltages at the beginning of each of said last mentioned intervals for developing a synchronizing pulse.

8. In a television system having means for receiving a continuous composite synchronizing signal composed of sequentially recurring groups of pulses, o-ne or more of said groups comprising pulses recurring at the line scanning frequency or an integral multiple thereof, another of said groups comprising pulses recurring at a higher integral multiple of said frequency, means for impressing said signal on a frequency responsive device adapted to .develop substantial voltages during receipt of said first mentioned groups and relatively low voltages during receipt of said last mentioned group, a thermionic amplifier having input and output circuits, means for biasing said input circuit in response to said voltages, and means responsive to current variations in said output circuit for developing field synchronizing pulses.

9. 1n a television system having means for receiving a continuous composite synchronizing signal composed of sequentially recurring pulse groups, certain of said groups being composed of pulses recurring at the line scanning frequency or an integral multiple thereof and synchronizing with successive scanning lines, said pulses containing a particular frequency component and harmonics thereof, another of said groups being composed of pulses recurring at a harmonic of said particular frequency and occurring within intervals between successive picture fields, means for impressing said signal upon a tuned circuit resonant at said particular frequency, said circuit having substantial voltages developed thereon only when said particular frequency is present in said signal, a thermionic device having a control grid and anode, means for detecting said voltages and biasing said grid in accordance therewith, an output impedance coupled to said anode, and means responsive tol change in anode current through said impedance for developing field synchronizing pulses.

l0. In a television system having means for receiving a continuous composite synchronizing signal composed of sequentially recurring groups of pulses, one of said groups comprising line synchronizing pulses having a fundamental frequency fh, another of said groups comprising equalizing pulses having a fundamental frequency 1min, Where k is an integer and n is the degree of interlace, and still another of said groups comprising vertical synchronizing pulses having a fundamental frequency plcnh, where pis an integer greater than one, means for impressing said signal upon two frequency responsive elements `tuned respectively to the frequencies knfh and plmfh, each of said elements being adapted to develop a substantial voltage thereon only at its resonant frequency, a thermionic device having at least two grids and an anode, means for biasing each of said grids in response to one of said voltages and in a sense to render said Idevice inoperative, said last means comprising a rectifier circuit energized from each element and coupled to one of said grids, whereby said device becomes operative and draws substantial anode current only when said groups of vertical synchronizing pulses are received, a vertical deflection generator, and means responsive to said anode current for synchronizing said generator.

ll. The method of synchronizing a plurality of different electrical effects at a receiving point with corresponding electrical effects at a transmitting point which comprises transmitting between said points a first wave containing a particular frequency component, interrupting the transmission of said wave at intervals, transmitting during said intervals a second wave having a fundamental frequency which is a higher frequency harmonic of said particular frequency, whereby said particular frequency is absent during said interruptions, synchronizing one of said effects with either of said frequencies, whereby said effect is synchronized continuously by one or another of said waves, and synchronizing another of said effects with the occurrence of the interruptions in said rst wave.

12. The method of controlling a plurality of electrical operations at a receiving point with waves transmitted over a single channel which comprises generating a plurality of periodic electrical waves at a transmitting point, all but one of said waves containing a particular frequency, said one wave having its lowest frequency higher than said particular frequency and harmonically related thereto, consecutively transmitting said waves over said channel in a predetermined sequence, effecting a first control operation continuously in response to receipt of any of said frequencies, and effecting a second, independent control operation in response to the disappearance of said particular frequency when said'one wave is transmitted. l

i3. The method of controlling a plurality of electrical operations at a receiving point with waves transmitted over a single channel which comprises generating a plurality of periodic electrical waves at a transmitting point, all but one of said waves containing a particular frequency, said one Wave having a fundamental frequency higher than said particular frequency and harmonically related thereto, consecutively transmitting said waves over said channel in a predetermined sequence, effecting a first control operation continuously in response to receipt of any of said frequencies, developing an electrical effect in response to receipt of said particular frequency, developing a control signal in response to transient changes in said effect upon disappearance of said particular frequency, and effecting a'second, independent control operation in response to said control signal.

lll, In the art of television, the method of synchronizing two different scanning operations at a receiving point with waves transmitted over a single channel which comprises generating a plurality of periodic electrical waves at a transmitting point, all but one of said waves containing a particular frequency, said one Wave having a fundamental frequency higher than said particular frequency and harmonically related. thereto, consecutively transmitting said waves over said channel in a predetermined regular sequence, each wave being interrupted when any other of said waves is transmitted, synchronizing one of said scanning operations continuously first by one and then another of said frequencies, and synchronizing the other of said scanning operations in response to the disappearance of said particular frequency when said one wave is transmitted.

15. In the art of television, the method of synchronizing the scanning actions of a television transmitter and receiver which comprises transmitting a wave containing a particular frequency component, interrupting the transmission of said wave at periodically recurring intervals, transmitting duringsaid intervals a wave having a fundamental frequency higher than said particular frequency and harmonically related thereto, whereby said particular frequency is absent during said intervals, receiving said waves, effecting line synchronization continuously first by one and then the other of said frequencies, and effecting field synchronization with the interruptions in said first wave in response to the disappearance of said particular frequency component.

16. The method ofv synchronizing a television transmitter and receiver which comprises generati'ng first synchronizing pulses recurring at the line scanning frequency or an integral multiple thereof, generating second synchronizing pulses recurring at a higher integral multiple of said line scanning frequency, transmitting said first pulses, interrupting the transmission of said first pulses for predetermined time intervals occurring between successive traversals of the picture field, transmitting said second pulses during said intervals, effecting line synchronization fiom any of said pulses, developing a control potential in response to receipt of a frequency component of said first pulses lower than the frequency of recurrence of said second pulses, deriving an individual and distinct synchronizing signal in response to transient changes in said control potential caused by the disappearance of said frequency component during said time intervals, and effecting field synchronization from said signal.

17. The method of synchronizing the scanning actions of a television transmitter and receiver which comprises transmitting first substantially rectangular synchronizing pulses recurring at the line scanning frequency or an integral multiple thereof, interrupting the transmission of said pulses at regular intervals, transmitting during said intervals second substantially rectangular synchronizing pulses recurring at a higher integral multiple of said line scanning frequency, effecting line synchronization in response to receipt of either of said pulses and effecting field synchronization in response to the occurrence of the interruptions in said first pulses.

18. A system for synchronizing the scanning actions of television transmitting and receiving apparatus comprising means for transmitting between said apparatus a rst wave containing a particular frequency component, means for periodically interrupting the transmission of said wave at intervals, means for transmitting during said intervals a second wave having a fundamental frequency higher tlian said particular frequency and harmonically related thereto, a line deflection generator adapted to be synchronized at either of said frequencies, means for impressing said waves on said generator to synchronize its operation, a field deflection generator adapted to be synchronized at the frequency of the interruptions in said first wave, and means responsive to the occurrence of said interruptions for synchronizing the operation of said field deflection generator.

19. A system for synchronizing the scanning actions of a television transmitter and receiver comprising means for transmitting first substantially rectangular synchronizing pulses recurring at the line scanning frequency or an integral multiple thereof, means for interrupting the transmission of said pulses at regular intervals, means for transmitting during said intervals second substantially rectangular synchronizing pulses recurring at a higher integral multiple of said line scanning frequency, a first deflection generator adapted to be synchronized at any of said frequencies, means for impressing said pulses on said generator to synchronize its operation, a second deflection generator adapted to be synchronized at the frequency of interruption of said first pulses, and means responsive to the occurrence of said interruptions for synchronizing the operation of said second generator.

20. In a system for synchronizing a television transmitter and receiver, means for generating first synchronizing pulses recurring at the line scanning frequency or an integral multiple thereof, means for generating second synchronizing pulses recurring at a higher integral multiple of said line scanning frequency, means for transmitting said first pulses, means for interrupting the transmission of said first pulses for predetermined time intervals occurring between successive traversals of the picture field and for transmitting said second pulses during said intervals, means for effecting line synchronization in response to receipt of any of said pulses, and means for effecting field synchronization in response to the disappearance of a component frequency of said first pulses during said intervals, said component frequency being lower than the frequency of recurrence of said second pulses.

2l. In a system for synchronizing a television transmitter and receiver, means for generating first synchronizing pulses recurring at the line scanning frequency or an integral multiple thereof, means for generating second synchronizing pulses recurring at a higher integral multiple of said line scanning frequency, means for transmitting said first pulses, means for interrupting the transmission of said first pulses for predetermined time intervals occurring between successive traversals of the picture field and for transmitting said second pulses during said intervals, means for effecting line synchronization in response to receipt of any of said pulses, means for developing a control potential in response to receipt of a component frequency of said first pulses lower than the frequency of recurrence of said second pulses, means for developing a synchronizing signal in response to transient changes in said control potential caused by the disappearance of said component frequency during said time intervals, and means for effecting field synchronization in response to said control signal.

22. In a television system, a synchronizing pulse generator for synthesizing a composite synchronizing signal comprising, in combination, means for generating first substantially rectangular synchronizing pulses recurring at the line scanning frequency or an integral multiple thereof and synchronized with successive scanning lines, means for transmitting said pulses to a signal channel, means for interrupting their transmission during predetermined time intervals occurring between successive picture elds, means for generating second substantially rectangular synchronizing pulses recurring at a higher integral multiple of said line scanning frequency, means for transmitting said second pulses to said channel only during said intervals, all said pulses being of substantially equal heights and of widths inversely proportional to their frequencies of recurrence, whereby the average amplitude of said composite signal transmitted to said channel is substantially constant.

EVERHARD H. B. BARTELINK. 

